Summary
Highlights
Infrared radiation is classified by wavelength: short-wave (770-1500 nm), near long-wave (1500-5000 nm), and far long-wave (5000-15000 nm). Short-wave infrared penetrates 1-10mm, near long-wave penetrates up to 5mm, while far long-wave does not penetrate skin tissue.
Infrared emitters are categorized by energy production and transmission. The first group includes hot water bottles and compresses, using conduction and convection (long waves). The second group, like electric blankets, uses conduction, convection, and radiation (long and short waves). The third group, incandescent lamps and the sun, uses radiation (short waves, visible, and UV light). The fourth group, high-frequency currents like shortwave and microwave diathermy, convert electrical energy into thermal energy.
Infrared can be produced by bulbs and lamps. Some bulbs have a red filter that absorbs white light, allowing only red and infrared radiation to pass through, ensuring all radiation is directed forward. Without a filter, white light also emits.
The impact zone of infrared radiation shows greater intensity at the center, diminishing outwards, governed by Lambert's cosine law. Perpendicular radiation provides greater intensity than angled radiation.
Bier's oven is another infrared emission device, a wooden structure with metallic elements and internal light bulbs (60 volts) that could be turned on in pairs via switches. These older devices had greater durability.
Infrared dosage depends on distance, angle (Lambert's law), exposure time, and patient subjectivity. Longer exposure increases the effect. The patient's comfort is paramount; the sensation should be pleasant.
Patients experience three types of sensations: moderate heat (pleasant and light), intense heat (tolerable with sweating), and intolerable heat (painful, burning, intense redness, and profuse sweating). Moderate heat is the desired sensation for therapy.